Fingerprint sensing device with interposer structure

Abstract

The invention relates to a fingerprint sensing device comprising: a sensing chip comprising an array of sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of the sensing elements and a finger placed on a sensing surface of the sensing device. A surface of the sensing elements defines a sensing plane. The sensing device further comprises a plurality of interposer structures arranged on the sensing chip extending above sensing plane, wherein the plurality of interposer structures have the same height above the sensing plane. A protective plate is attached to the sensing chip by means of an adhesive, and the protective plate rests on the interposer structures such that a distance between the protective plate and the sensing plane is defined by the height of the interposer structures.

The invention claimed is: 
     
       1. A fingerprint sensing device comprising:
 a sensing chip comprising an array of sensing elements, said sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of said sensing elements and a finger placed on a sensing surface of said sensing device, wherein a surface of said sensing elements define a sensing plane; 
 a plurality of interposer structures arranged on said sensing chip extending above said sensing plane, wherein said plurality of interposer structures have the same height above said sensing plane; and 
 a protective plate attached to said sensing chip by means of an adhesive arranged on said sensing chip, wherein said protective plate rests on said interposer structures such that a distance between said protective plate and said sensing plane is defined by the height of said interposer structures. 
 
     
     
       2. The sensing device according to  claim 1 , wherein a variation in height between said plurality of interposer structures is less than 1 μm. 
     
     
       3. The sensing device according to  claim 1 , wherein said plurality of interposer structures comprises parallel lines. 
     
     
       4. The sensing device according to  claim 3 , wherein said parallel lines are aligned with an edge of said sensing chip and have a length substantially similar to a side of the sensing chip. 
     
     
       5. The sensing device according to  claim 1 , wherein said plurality of interposer structures comprises one interposer structure centered on each of said sensing elements. 
     
     
       6. The sensing device according to  claim 5 , wherein said plurality of interposer structures are formed in a material having a dielectric constant higher than a dielectric constant of said adhesive. 
     
     
       7. The sensing device according to any one of  claim 1 , wherein said plurality of interposer structures are arranged in alignment with boundaries between said sensing elements, such that a central portion of each sensing element is not covered by an interposer structure. 
     
     
       8. The sensing device according to  claim 7 , wherein said plurality of interposer structures are formed in a material having a dielectric constant lower than a dielectric constant of said adhesive. 
     
     
       9. The sensing device according to  claim 1 , wherein said interposer structures are arranged on said sensing chip at locations outside of a sensing area of said sensing chip, said sensing area being defined by said array of sensing elements. 
     
     
       10. The sensing device according to  claim 1 , wherein said interposer structures are arranged to form a frame partially surrounding the array of sensing elements. 
     
     
       11. The sensing device according to  claim 10 , further comprising a space between adjacent interposer structures of said frame enabling a liquid adhesive to flow out through gaps formed between the structures when said liquid adhesive is deposited. 
     
     
       12. The sensing device according to  claim 10 , wherein the adhesive is arranged within the frame formed by said interposer. 
     
     
       13. The sensing device according to  claim 10 , wherein the adhesive is arranged to completely cover the array of sensing elements. 
     
     
       14. The sensing device according to  claim 1 , wherein said plurality of interposer structures comprises a photoresist. 
     
     
       15. The sensing device according to  claim 1 , further comprising a bond wire arranged between a bond pad on said sensing chip and a substrate on which the sensing chip is arranged, wherein a bond loop height of said bond wire is lower than said interposer structure. 
     
     
       16. The sensing device according to  claim 1 , further comprising a via connection through said sensing chip to electrically connect said sensing chip to a substrate. 
     
     
       17. An electronic device comprising a sensing device according to  claim 1 .